PESHAWAR, Pakistan – A suicide bomber blew up his explosives-filled car Saturday at a police checkpoint in the northwestern Pakistani city of Peshawar, killing at least 11 people, officials said.

In the second suicide strike to hit the troubled city in two days, the bomber detonated when police asked him to stop for a search, Peshawar district administration chief Sahibzada Anis told AFP.

The latest in a spate of devastating attacks comes as 30,000 troops press their most ambitious assault yet against Taliban militants in their mountain strongholds on the Afghan border.

"At least 11 people have been killed and 26 others wounded," Anis told AFP, adding three women, three children and five men were killed in the blast.

Peshawar police chief Liaqat Ali Khan told AFP that two policemen were among the dead.

Malik Jehangir, in charge of the checkpoint, told AFP policemen were checking vehicles when he saw a suspicious black car across the barrier and asked one of the policemen to go and check it.

"I saw that there was some argument between the driver and the policeman and suddenly a blast downed me with shrapnel piercing my shoulder," he said.

Another witness, Akbar Ali, said he was riding a motorcycle and waiting in the queue at the checkpoint when he saw a scuffle between the bomber and the policeman. Seconds later a huge blast threw him to the ground.

Television footage showed a massive plume of smoke above the Pushta Khara neighbourhood, on the outskirts of Peshawar, and the wreckage of several cars.

The city, on the edge of Pakistan's Al-Qaeda and Taliban-infested tribal belt, has increasingly become the favoured target for attacks by militants, particularly since the army launched its offensive in October.

On Friday a suicide attack there devastated the three-storey provincial headquarters of the Inter Services Intelligence (ISI), which is heavily involved in Pakistan's anti-terror fight.

At least 17 people were killed and 39 others injured in that bombing, officials said.

Also Friday, eight people were killed in a suicide blast in the garrison town of Bannu, southwest of Peshawar, police said.

The most devastating bomb attack in Pakistan in two years killed at least 118 people in a crowded Peshawar market on October 28 as militants put ordinary civilians in the crosshairs of their bloody campaign.

The government blames increasing attacks on Tehreek-e-Taliban Pakistan (TTP), which is the target of the ongoing offensive and which wants to avenge the killing of their leader Baitullah Mehsud by a US missile in August.

The Friday and Saturday attacks were claimed by the TTP, which warned of more strikes to come.

"We claim responsibility for the ISI, Bannu and Peshawar checkpost suicide attacks. We will launch so many attacks that the president, prime minister and governor would not be able to sit in their palaces," TTP spokesman Azam Tariq told AFP.

Qari Hussain, a TTP leader, said on Saturday the attacks were in reaction to the "military operation in South Waziristan and government policies."

"We will launch more suicide attacks," he told AFP.

Pakistan launched a punishing air and ground offensive in South Waziristan tribal district on October 17, with 30,000 troops backed by fighter jets and helicopter gunships.

The military said in a statement Saturday that during the past 24 hours it had killed seven Taliban militants as troops consolidated positions and conducted search operations in former militant strongholds.

And in northwestern Swat valley, troops killed 13 insurgents in two separate gunfights Saturday, officials said.